Fuel injector for auto-ignition internal combustion engines

ABSTRACT

A fuel injection nozzle for self-igniting internal combustion engines, having a nozzle body, in which a conical seat face from which injection ports originate is formed at the bottom of a blind bore. A valve needle which is guided displaceably with a guide portion in the inlet region of the blind bore counter to a closing force and counter to the fuel flow direction and on the end of a valve shaft adjoining the guide portion has a closing cone cooperating with the seat face. The valve shaft circumferentially defines an annular chamber for fuel delivery, and is characterized in that in a transitional region between the valve shaft and the closing cone, a throttle device of variable throttle cross section is disposed, by which the injection cross section can be varied as a function of the axial displacement of the valve needle.

PRIOR ART

The invention relates to a fuel injection nozzle for self-ignitinginternal combustion engines, having a nozzle body, in which a conicalseat face from which injection ports originate is formed at the bottomof a blind bore. A valve needle which is guided displaceably with aguide portion in the inlet region of the blind bore counter to a closingforce and counter to the fuel flow direction and on the end of a valveshaft adjoining the guide portion has a closing cone cooperating withthe seat face. The valve shaft circumferentially defines an annularchamber for fuel delivery. Such fuel injection nozzles are disclosed forinstance in German published, non-examined Patent Application DE-OS 3734 587 and German Utility Model 93 0 992.0.

In the fuel injection nozzle disclosed by DE-OS 37 34 587, in order toprevent the so-called blowback of the combustion gases, a controlpassage for the injection fuel is provided that is varied by the valveneedle as a function of the stroke and whose flow cross sectiondecreases in the closing stroke of the valve needle, down to a throttlecross section that decouples the relief wave on the pump side from thefuel pressure in the blind bore.

In the fuel injection nozzle disclosed in German Utility Model 93 01992.0, a guide sleeve that surrounds the valve shaft and has a conicallyembodied face end and, in its portion near the conical face end, aplurality of recesses extending as far as the conical face end preventsthe closing cone from covering some or all of the injection ports as aconsequence of play or eccentricity of the valve needle, or if lateralforces in a short opening stroke act on the valve needle, which coveragewould impair the combustion process.

One problem of such fuel injection nozzles is that even a short strokeof the valve needle results in large flow quantities. Especially in thepre-stroke range, the stroke-dependent characteristic curve of the flowis very steep.

Aside from deleterious combustion events, this is also problematicbecause different fuel injection nozzles with different tolerances thusproduce very different flow quantities, with the same stroke.

It has furthermore been demonstrated that a graduated injection, or atleast one that increases slowly at the injection onset, in general leadsto an improvement in the emissions figures of the engines.

It is therefore the object of the invention to refine a fuel injectionnozzle of this generic type in such a way that an aforementionedproduction tolerances, particularly in the range of the prestroke, donot deleteriously affect the injection event, and that at least at theinjection onset, a slowly increasing injection is attained.

ADVANTAGES OF THE INVENTION

This object is attained, in a fuel injection nozzle of the typedescribed at the outset, in that in the transitional region between thevalve shaft and the closing cone, a throttle device of variable throttlecross section is disposed, by which the injection cross section can bevaried as a function of the axial displacement of the valve needle.

The disposition of this kind of throttle device has the particularlygreat advantage that not only can the injection cross section be variedthereby in such a way that it increases continuously at the onset of theinjection event, but also that the injection cross section can be variedin such a way that particularly in the prestroke range, only slight flowchanges occur during a stroke motion of the valve needle, and as aconsequence, production tolerances are much less disruptive than inknown fuel injection nozzles.

As to the embodiment of the throttle device, the most various versionsare conceivable.

One advantageous version provides that the throttle device includes ashoulder, formed in the annular chamber, and a control edge disposedadjacent to it and spaced apart from it on the valve shaft, whichcontrol edge is adjoined downstream by at least one conical face. Bymeans of the shoulder, the control edge spaced apart from it, and the atleast one conical face adjoining the control edge downstream thereof, athrottle with a throttle cross section that decreases as a result ofaxial displacement of the valve needle is made possible in a way that ishighly advantageous, because it is technologically easy to accomplish.

One advantageous version provides that the control edge substantiallyfaces the shoulder. As a result, a defined initial throttle crosssection is advantageously realized.

In another advantageous version, the control edge is disposed slightlydownstream of the shoulder. As a result, upon a slight axialdisplacement, the initial throttle cross section is kept unchanged atfirst, until the control edge overtakes the shoulder.

With regard to the conical face adjoining the control edge, once againthe most various versions are conceivable.

The conical face is advantageously defined as a function of thedisposition of the control edge opposite the shoulder.

Thus one advantageous version provides that the conical face adjoiningthe control edge has a smaller cone angle than the conical seat face. Asa result, in cooperation with the initial throttle cross sectiondetermined by the spacing of the control edge from the shoulder, aninitial throttling of the injected fuel quantity is attained in whichthe conical seat face of the valve needle is also, in a highlyadvantageous way, included in the throttling process.

It is moreover also possible for the conical face adjoining the controledge to have a larger cone angle than the conical seat face.

In a further exemplary embodiment of a throttle device, which isadvantageous in terms of its manufacture, it is provided that a sleeveaxially displaceable counter to the restoring force of a spring isdisposed in the annular chamber and rests with a conically embodied faceend on the outer annular face of the conical seat face, and in it, atleast two openings of different opening cross sections are provided thatcan be uncovered in succession by axial displacement of the valveneedle. Such a sleeve has the very great advantage in particular that itis not only easy to make but is also easy to assemble, especially evenoutside the nozzle body.

As to the disposition and embodiment of the openings of differentopening cross section that can be uncovered in succession by axialdisplacement of the valve needle, they can purely in principle have themost various shapes. One advantageous version provides that a firstopening is disposed above a control edge, formed on the valve shaft, inthe jacket of the sleeve, and a second opening whose opening crosssection is smaller than that of the first opening is disposed below thecontrol edge embodied on the valve shaft. The opening provided in theconical face then thus takes on the task of initial throttling, whileconversely the opening provided in the jacket enables a valve needlestroke- dependent decrease in the throttle cross section as a result ofaxial displacement of the valve needle. The opening provided in thejacket may be elliptical, oval, round, triangular, quadrilateral, orpolygonal in shape.

In another advantageous version it is provided that two rows ofperforations one above the other are disposed in the jacket of thesleeve, and the downstream row of perforations has a smaller totalopening cross section than the upstream row of perforations. Thisversion of the throttle device advantageously enables filtering of theinjected fuel cross section.

Another advantageous version provides that a sleeve axially displaceablecounter to the restoring force of a spring is disposed in the annularchamber and rests with a conically embodied face end on the outerannular face of the conical seat face and that facing the sleeve in thevalve shaft is at least one recess, cooperating with the sleeve, whoseopening cross section, on the end of the sleeve toward the guideportion, increases steadily toward the conical seat face.

Yet another advantageous version provides that a sleeve which can beslaved by an axial displacement of the valve needle and is axiallydisplaceable counter to the restoring force of a spring is disposed inthe annular chamber and rests with a conically embodied face end on theouter annular face of the conical seat face, and its conically embodiedface end has at least one recess that is open toward the face end.

In this last version, the sleeve is especially easy to make, with only afew production steps.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention are the subjectof the ensuing description and are shown in several exemplaryembodiments in the drawings.

Shown in the drawings are:

FIG. 1, in a half-sectional view and partly cut away, two exemplaryembodiments of a fuel injection nozzle that makes use of the invention;

FIG. 2, each in a half-sectional view and partly cut away, two furtherexemplary embodiments of a fuel injection nozzle that makes use of theinvention;

FIG. 3, a half-sectional view of a throttle device of a fuel injectionnozzle that makes use of the invention;

FIG. 3a, an enlarged detail of the throttle device shown in FIG. 3;

FIG. 4, each in a half-sectional view and partly cut away, two furtherexemplary embodiments of a fuel injection nozzle according to theinvention;

FIG. 5, each in a half-sectional view and partly cut away, two furtherexemplary embodiments of a fuel injection nozzle according to theinvention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The lower region of an exemplary embodiment of a fuel injection nozzlefor self-igniting internal combustion engines is shown in the left halfof FIG. 1.

As seen in FIG. 1, the fuel injection nozzle has a nozzle body 30, inwhich a conical seat face 32 at which injection ports 34 originate isformed in the bottom of a blind bore 37. A valve needle is disposedaxially displaceably in the blind bore 37; it is guided axiallydisplaceably, counter to a closing force and counter to the fuel flowdirection, by a guide portion (not shown) in the inlet region of theblind bore and on the end of a valve shaft 10 adjoining the guideportion the injection nozzle has a closing cone 12 that cooperates withthe seat face 32.

The valve shaft 10 circumferentially defines an annular chamber 40,which serves to deliver fuel. In the transitional region between thevalve shaft 10 and the closing cone 12, a throttle device of variablethrottle cross section is disposed; by means of the throttle, theinjection cross section can be varied as a function of the axialdisplacement of the valve needle. The throttle device includes ashoulder 31, formed in the annular chamber on the nozzle body 30, whichnarrows the annular chamber 40 to a smaller cylindrical portion 33,disposed downstream of the shoulder 31 in the blind bore 37 and acontrol edge 20, embodied slightly downstream on the valve shaft 10 ofthe valve needle, and two conical faces 21, 22 with different coneangles adjoin this control edge downstream of it.

The function of such a throttle device of variable throttle crosssection is as follows: First, a first throttle cross section is realizedby means of the spacing between the shoulder 31 and the control edge 20,and hence between the shoulder 31 and the valve shaft 10. By axialdisplacement of the valve shaft 10 counter to the flow direction of thefuel to be injected, or in other words upward in terms of FIG. 1, thethrottle cross section initially does not change, until the control edge20 has executed a stroke motion marked U in FIG. 1 and the control edgeovertakes the shoulder 31. At that moment, the first conical face 21 isfacing the shoulder 31, which because of its conicity leads to aincrease in the throttle cross section upon a further axial displacementof the valve needle.

This throttle cross section increases still further as soon as thesecond conical face 22 begins to overtake the shoulder 31, so that withthe further opening stroke motion of the valve needle, the overflowcross section from the annular chamber 40 to the injection ports 34increase.

The exemplary embodiments shown in the right half of FIG. 1 and in theleft and right halves of FIG. 2 differ from the above-describedexemplary embodiment shown in the left half of FIG. 1 in that thecontrol edge 20 and shoulder 31 are disposed differently. Those elementsthat are identical to those of the first exemplary embodiment shown inthe left half of FIG. 1 are identified by the same reference numerals,and so the entire content of the description of the first exemplaryembodiment is referred to for their description as well.

A further exemplary embodiment of a throttle device of variable throttlecross section, which is used particularly in injection nozzles forcommon rail injection systems, is shown in FIG. 3 and FIG. 3a.

In FIG. 3, those elements that are identical to those of the exemplaryembodiments shown in the FIGS. 1 and 2 are identified by the samereference numerals, and so for their description, the descriptions ofthese exemplary embodiments are again referred to. The exemplaryembodiment of a common rail fuel injection nozzle shown in FIG. 3differs from the valve seat, known per se, used in common rail nozzles.The exemplary embodiment shown in FIG. 3 also differs from the exemplaryembodiments shown in FIGS. 1 and 2 in that the control edge 20 embodiedon the valve needle 10 faces the shoulder 31, formed on the valve body30, substantially directly, being spaced apart from it by a distance d1.The control edge 20 is adjoined by a conical face 23, whose cone angleδ1 is smaller than the angle δ2 of the closing cone. Because of the gapformed by the spacing d1, the transition from the opening range to theprestroke range of the fuel injection nozzle is defined. This transitioncan also be varied by disposing the control edge 20 slightly below theshoulder 31 at a spacing h2.

By embodying the throttle device in this way, the closing cone 12 isincluded in the throttling function of the throttle device, as will nowbe described.

The function of the fuel injection nozzle shown in FIG. 3 and FIG. 3a isas follows: Initially, the closing cone 12 lifts slightly away from thevalve seat 32, causing a gap to form between the closing cone 12 and thevalve seat 32, the width of the gap being less than the spacing d1between the control edge 20 and the shoulder 31. Because of thesespacing ratios, the gap between the closing cone 12 and the valve seat32 initially forms a throttle. Upon further axial displacement of thevalve needle, the gap between the closing cone 23 and shoulder 31 onvalve body 30 slowly becomes continuously and increasingly larger,approximately until such time as the conical face 23 adjoining thecontrol edge 20 moves past the shoulder 31, or in other words until thevalve needle 10 has executed an axial stroke of height h1. As a result,with an increasing stroke of the valve needle, a shallow rise in theinjection cross section is made possible, this rise becoming greater asthe axial stroke lengthens further, once the axial stroke of magnitudeh1 has been executed.

As a result, not only is shaping of the injection course in anespecially advantageous way made possible, but in particulardisadvantageous deviations in the injection cross section because ofproduction tolerances are eliminated.

Further exemplary embodiments of throttle devices for fuel injectionnozzles are shown in FIGS. 4 and 5, in each case in a half-sectionalview.

In the exemplary embodiments shown in FIGS. 4 and 5, those elements thatare identical to those of the exemplary embodiments described above areidentified by the same reference numerals, and for their description,once again the above descriptions of these exemplary embodiments arereferred to. The exemplary embodiments shown in FIGS. 4 and 5 differfrom the exemplary embodiments shown in FIGS. 1-3 in that instead of theembodiment of a shoulder 31 in the annular chamber 40, a sleeve 50axially displaceably counter to the restoring force of a spring (notshown) is disposed in the annular chamber and rests with a conical faceend on the outer annular face 32 a of the conical seat face 32.

In the case of the sleeve 50 shown in the left half of FIG. 4, twoopenings 52 and 53 that can be uncovered in succession by axialdisplacement of the valve needle are provided in the sleeve, of whichthe first opening 52 is disposed in the jacket of the sleeve 50 and thesecond opening 53 is provided, for instance in the form of grooves, onthe conically embodied face end 51. A control edge 70 is provided on thevalve shaft 10; when the fuel injection nozzle is closed, this controledge is disposed at a predetermined spacing U below the first opening 52having the larger opening cross section. In such a fuel injectionnozzle, the opening 53 provided in the conical end face 51 initiallyacts as a throttle, which upon a slight axial displacement of the valveshaft 10 leads to an injection cross section determined by the openingcross section of the second opening 53. Upon a further axialdisplacement of the valve shaft 10, the control edge 70 overtakes theopening 52 of larger opening cross section disposed in the jacket of thesleeve 50, and as a result the injected fuel quantity increasescontinuously as the stroke motion of the valve shaft 10 lengthens.

In the exemplary embodiment shown in the right half of FIG. 4, the twoopenings of different opening cross sections are each formed by one rowof perforations 61, 62; the downstream row of perforations 61 has asmaller total cross section than the upstream row of perforations 62.

In this case, the control edge 70 is located between the first andsecond rows of perforations 61, 62. By axial displacement of the valveshaft 10, the control edge 70 overtakes the upstream row of perforations62 and opens it continuously as the stroke motion lengthens, and as aresult the throttle cross section increases in size continuously as thestroke of the valve shaft 10 continues.

The exemplary embodiment shown in the left half of FIG. 5 differs fromthe exemplary embodiment shown in FIG. 4 in that a plurality of recesses80 cooperating with the sleeve 50 are disposed facing the sleeve 50 inthe valve shaft 10, and their opening cross section increasescontinuously toward the conical seat face on the end of the sleeve 50remote from the closing cone 12 and oriented toward the guide portion(not shown) of the valve needle. This region 81 acts as a throttle ofvariable throttle cross section, which is increases continuously by astroke motion of the valve shaft 10 in its opening direction.

In the exemplary embodiment shown in the right half of FIG. 5, thesleeve 50 is embodied such that it can be slaved by the valve shaft 10by means of an axial displacement of the valve needle and thus of thevalve shaft 10. To that end, the valve shaft 10 has a shoulder 17, whichengages a protrusion 57 of the sleeve 50. In its conical face end 51,the sleeve So has recesses 55, which are open toward the face end andwhich act as a throttle cross section that does not change withincreasing axial displacement of the valve shaft 10, until aftershoulder 17 engages prostrusion 57. As shown in FIG. 5, the protrusion57 is spaced apart from the shoulder 17 formed on the valve needle 10 insuch way that the sleeve 50 is initially not slaved upon a stroke motionof the valve needle. In that case, the injected fuel quantity is guidedby the openings 55 formed in the conical face end 51, which perform athrottling function.

The spacing of the protrusion 57 above the shoulder 17 is equivalent toa prestroke V of the fuel injection nozzle.

The above description pertains to an injection port nozzle, but it isunderstood that the invention is not limited to such an injection portnozzle and can be used in a blind bore nozzle as well, in acorresponding way.

The forgoing relates to a preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A fuel injection nozzle for self-ignitinginternal combustion engines, comprising a nozzle body (30), in which aconical seat face (32) is formed from which injection ports (34)originate at a bottom of a blind bore (37), a valve needle has a closingcone (12) that cooperates with the valve seat face (32), said valveneedle is guided displaceably with a guide portion in a inlet region ofthe blind bore (37) counter to a closing force and counter to a fuelflow direction and on an end of a valve shaft (10) adjoining the guideportion, the valve shaft (10) circumferentially defining an annularchamber (40) for fuel delivery, in a transitional region between thevalve shaft (10) and the closing cone (12), a throttle device ofvariable throttle cross section is disposed, in which the throttledevice includes a shoulder (31), formed in the annular chamber (40), anda control edge (20) disposed adjacent to the shoulder and spaced apartfrom the shoulder on the valve shaft (10), said control edge is adjoineddownstream by at least one conical face (21, 22), by which the injectioncross section is varied as a function of an axial displacement of thevalve needle.
 2. The fuel injection nozzle in accordance with claim 1,in which the control edge (20) substantially faces the shoulder (30). 3.The fuel injection nozzle in accordance with claim 2, in which the atleast one conical face (21, 22) adjoining the control edge (20) has asmaller cone angle than the conical seat face (20).
 4. The fuelinjection nozzle in accordance with claim 2, in which the at least oneconical face (21, 22) adjoining the control edge (20) has a larger coneangle than the conical seat face (20).
 5. The fuel injection nozzle inaccordance with claim 1, in which the control edge (20) is disposedslightly downstream of the shoulder (31).
 6. The fuel injection nozzlein accordance with claim 5, in which the at least one conical face (21,22) adjoining the control edge (20) has a smaller cone angle than theconical seat face (20).
 7. The fuel injection nozzle in accordance withclaim 5, in which the at least one conical face (21, 22) adjoining thecontrol edge (20) has a larger cone angle than the conical seat face(20).
 8. A fuel injection nozzle for self-igniting internal combustionengines, comprising a nozzle body (30), in which a conical seat face(32) is formed from which injection ports (34) originate at a bottom ofa blind bore (37), a valve needle has a closing cone (12) thatcooperates with the valve seat face (32), said valve needle is guideddisplaceably with a guide portion in a inlet region of the blind bore(37) counter to a closing force and counter to a fuel flow direction andon an end of a valve shaft (10) adjoining the guide portion, the valveshaft (10) circumferentially defining an annular chamber (40) for fueldelivery, in a transitional region between the valve shaft (10) and theclosing cone (12), a throttle device of variable throttle cross sectionis disposed, by which the injection cross section is varied as afunction of an axial displacement of the valve needle, in which a sleeve(50) axially displaceable counter to the restoring force of a spring isdisposed in the annular chamber (40) and rests with a conically embodiedface end (51) on an outer annular face (32 a) of the conical seat face(32), and at least two openings (52, 53; 61, 62) of different openingcross section are provided in said sleeve (50) in which the opening areuncovered in succession by axial displacement of the valve needle. 9.The fuel injection nozzle in accordance with claim 8, in which a firstopening (52) is disposed above a control edge (70), formed on the valveshaft, in the jacket of the sleeve (50), and a second opening (53) ofsmaller opening cross section than that of the first opening (52) isdisposed in the face end (51) embodied on the sleeve (50).
 10. The fuelinjection nozzle in accordance with claim 8, in which two rows ofperforations (61, 62) one above the other are disposed in the jacket ofthe sleeve (50), and the downstream row of perforations (61) has asmaller total opening cross section than the upstream row ofperforations (62), and a control edge (70) formed on the valve shaft(10) is disposed, in the closed state of the fuel injection valve,between the two rows of perforations (61, 62).
 11. A fuel injectionnozzle for self-igniting internal combustion engines, comprising anozzle body (30), in which a conical seat face (32) is formed from whichinjection ports (34) originate at a bottom of a blind bore (37), a valveneedle has a closing cone (12) that cooperates with the valve seat face(32), said valve needle is guided displaceably with a guide portion in ainlet reason of the blind bore (37) counter to a closing force andcounter to a fuel flow direction and on an end of a valve shaft (10)adjoining the guide portion, the valve shaft (10) circumferentiallydefining an annular chamber (40) for fuel delivery, in a transitionalregion between the valve shaft (10) and the closing cone (12), athrottle device of variable throttle cross section is disposed, by whichthe injection cross section is varied as a function of an axialdisplacement of the valve needle, in which a sleeve (50) axiallydisplaceable counter to the restoring force of a spring is disposed inthe annular chamber (40) and rests with a conically embodied face end onthe outer annular face (32 a) of the conical seat face (32) and thatfacing the sleeve (50) in the valve shaft (10) is at least one recess(80), that cooperates with the sleeve (50), whose opening cross section,on the end of the sleeve (50) toward the guide portion, increasessteadily toward the conical seat face.
 12. A fuel injection nozzle forself-igniting internal combustion engines, comprising a nozzle body(30), in which a conical seat face (32) is formed from which injectionports (34) originate at a bottom of a blind bore (37), a valve needlehas a closing cone (12) that cooperates with the valve seat face (32),said valve needle is guided displaceably with a guide portion in a inletregion of the blind bore (37) counter to a closing force and counter toa fuel flow direction and on an end of a valve shaft (10) adjoining theguide portion, the valve shaft (10) circumferentially defining anannular chamber (40) for fuel delivery, in a transitional region betweenthe valve shaft (10) and the closing cone (12), a throttle device ofvariable throttle cross section is disposed, by which the injectioncross section is varied as a function of an axial displacement of thevalve needle, in which a sleeve (50), which is slaved by an axialdisplacement of the valve needle and is axially displaceable counter tothe restoring force of a spring is disposed in the annular chamber (40)and rests with a conically embodied face end (51) on the outer annularface (32 a) of the conical seat face (32), and its conically embodiedface end (51) has at least one recess (55) that is open toward the faceend.
 13. A fuel injection nozzle for self-igniting internal combustionengines, comprising a nozzle body (30), in which a conical seat face(32) is formed from which injection ports (34) originate at a bottom ofa blind bore (37), a valve needle has a closing cone (12) thatcooperates with the valve seat face (32), said valve needle is guideddisplaceably with a guide portion in a inlet region of the blind bore(37) counter to a closing force and counter to a fuel flow direction andon an end of a valve shaft (10) adjoining the guide portion, the valveshaft (10) circumferentially defining an annular chamber (40) for fueldelivery, in a transitional region between the valve shaft (10) and theclosing cone (12), a throttle device of variable throttle cross sectionis disposed, in which the throttle device includes a shoulder (31),formed in the annular chamber (40), and a control edge (20) disposedadjacent to the shoulder and spaced apart from the shoulder on the valveshaft (10), said control edge is adjoined downstream by at least oneconical face (21, 22), by which the injection cross section is varied asa function of an axial displacement of the valve needle, wherein thethrottle device includes a cylindrical portion (33) in the blind bore,and disposed downstream of the shoulder (31).